If using it you still encounter the NPE, ideally you could also try with our 19.1 or 20.0. SDK.If you still have problems maybe you can send a sample XML document + full XML Schema to us (support@oxygenxml.com) and we can look into this.We will no longer make any fixes on the 18.1 SDK though, maybe we can try to fix this in the 19.1 SDK although I cannot promise we'll have a release for it either but it's a possibility.